1. Field of the Invention
This invention relates generally to heat transfer, and, more particularly, to heatsink assemblies to remove at least some of the heat produced by a heat source, such as an electronic component.
2. Description of Related Art
Electronic components such as integrated circuits or semiconductor chips, hereafter referred to as xe2x80x9cchipsxe2x80x9d, are well known and commonly used in the art to perform electronic functions. When in use, the chips often produce significant levels of heat. To reduce the heat generated, the chip size needs to be decreased which causes the heat to be concentrated into a smaller area. As technology has increased the capacity of the chips to perform functions, it has been found that the amount of concentrated heat produced has increased significantly. The increased level of heat produced by chips during their use can lead to a number of problems; for example, elevated levels of heat can potentially cause the chip to malfunction.
Various methods have been employed in the art to dissipate heat from chips. One method involves creating a forced airflow across the chip using a fan or blower. Another method involves mounting a heatsink on the surface of the chip. Heatsinks are typically manufactured from a metal having a high thermal conductivity, such as aluminum, and are mounted onto the surface of the chip to dissipate the heat produced by means of thermal conduction. Heatsinks typically comprise a plurality of parallel fins that are mounted on a base and which serve to facilitate the radiation and convection of the conducted heat by providing increased surface area. Copper is a better conductor of heat than aluminum, but a pure copper heatsink is seldom used due to cost and weight constraints. Often a fan or blower will be used to provide a forced airflow across the heatsink fins to increase their heat transfer capacity.
The two most significant modes of heat transfer are heat conduction and heat convection. Heat conduction is the transfer of heat through a solid medium. Heat conduction can be through a single solid medium or can be from one solid medium to another adjacent solid medium. The transfer of heat is based on a temperature differential, i.e. heat flowing from a hot end to a cold end, until temperature equilibrium between the ends is reached. Heat convection is the transfer of heat away from a hot solid medium to a cooler body of air. The air, typically ambient, has a generally constant temperature. Heat is convected away by the air currents generated by the warming of the air near the hot solid medium, or by a forced flow of air past the hot solid medium. Both conduction and convection are useful in providing heat dissipation from electrical devices.
The network of heat transfer pathways through which heat must flow determines the overall heat transfer characteristics. The heat must be conducted away from the chip and through the various thermal pathways to reach an outer surface of the heatsink that is exposed to the air where it can then be convected away from the outer surface to the ambient air body.
Each material has its own unique thermal characteristics, one of which is thermal conductivity. The thermal conductivity of a material determines the heat transfer capability through that material. Some materials, such as metals, have high thermal conductivity, while other materials such as glass or rubber have low thermal conductivity. Materials having low thermal conductivity are generally known as thermal insulators. Some commonly used semiconductor materials, such as glass and glass ceramic composites, have low thermal conductivities and therefore hinder the dissipation of heat.
As new semiconductor designs are becoming smaller and are capable of increased processing capacity, the amount of concentrated heat generated has increased dramatically. The commonly used methods of cooling that are mentioned above have sometimes been found to be inadequate for cooling high performance chips. Current aluminum heatsink designs often cannot dissipate heat from the chip fast enough. To compound the problem, very large scale integrated circuit chips are often mounted in close proximity to other heat generating chips on a printed circuit board, and frequently the circuit board is itself disposed within a confined area of an electronic device. Chips located in close proximity to each other will act as secondary heat sources on each other by radiant heat transfer, thereby increasing the amount of heat dissipation needed, while at the same time elevating the air temperature surrounding the chips, which acts to restrict the rate of total heat transfer.
Another area of concern with a heatsink design is airflow. The flow of air from a conventional circular fan blade creates an uneven airflow pattern, which often includes a xe2x80x9cdead-zonexe2x80x9d in the area that is not covered by the fan blades, i.e. the center of the motor for most fans. In a typical design, the heatsink and fan combination will be centered on the chip die, which is the primary heat source of the chip. Therefore, the hottest portion of the heatsink, which is located directly above the die, will often receive the least amount of airflow, creating a location on the heatsink having a heat concentration, or a xe2x80x9chot spotxe2x80x9d.
Another heatsink design sometimes used comprises a flat copper bottom segment that is attached to the main aluminum heatsink segment. This design attempts to balance the increased heat transfer capabilities of copper with the increased cost associated with its use. Heat is conducted away from the chip by the copper segment, then from the copper segment to the aluminum segment, and finally to the surface of the fins where the heat is convected to the air. Copper, having a thermal conductivity approximately double that of aluminum, can remove heat faster from the chip surface, thus aiding the chip cooling effort. But a flat copper plate often cannot distribute the heat from a localized source evenly across its surface, thereby resulting in a heat concentration, sometimes referred to as a hot spot, at the location of the heat source. A location on the heatsink having a hot spot can make the airflow patterns, and therefore the fan position, critical for adequate heat dissipation.
Having the airflow pattern and/or fan position as a critical factor in the ability of a chip to function properly is an undesired limitation on the ability to manufacture and package the chip within an electrical device. When the total packaging of a device can comprise numerous chips and other components confined within a very limited space, efficient heat dissipation with a reduced number of hot spots is desired.
There exists a need for an improved heatsink design that can quickly and effectively conduct heat away from the semiconductor chip and convect the heat to the air, while also minimizing hot spots within the heatsink.
One embodiment of the present invention is a heatsink assembly comprising a first section having a first surface and a second surface. The first surface is adapted to contact a surface of a heat source and the second surface has a generally convex curvature. A second section also has a first surface and a second surface, the first surface comprising a concave curvature and in contact with the second surface of the first section. A plurality of fin elements protrude from the second surface of the second section.
Another embodiment of the invention is a method for cooling a heat source by providing a heatsink comprising a core segment having a first surface adapted to contact the heat source and a second surface having a generally convex curvature and having a greater surface area than the first surface. An outer segment has a first surface with a generally concave curvature adapted to contact the second surface of the core segment, and a second surface having a plurality of fin elements protruding from it. The heatsink is attached to the heat source. The heat source is cooled by conducting heat from the heat source to the core segment, through the core segment in a radial direction to the greater surface area of the second surface of the core segment, and to the outer segment. From the outer surface heat is conducted to the fin elements and convected to a surrounding air mass.